In many production operations, for instance the production of metal strip or plate, it is necessary to cut or split the metal strip or plates, in particular to trim the longitudinal edges of metal strip or plates. The apparatus for doing this can be trimming shears having at least two rotating circular blades. Normally, a trimmer has at least one trimming head or set of trimming shears on each side of the strip. This is because metal strip or metal plate is produced with somewhat ragged edges and then is trimmed so as to achieve a constant predefined strip or plate width and to remove the uneven strip or plate edges. Trimming metal strip is frequently done in processing lines in a continuous process with trimming heads provided on both sides of the strip. The trimming heads or trimming shears have circular blades rotated about parallel horizontal axes extending horizontally transversely to the strip and its longitudinal travel direction. At least one of the blades of each trimmer is movable axially and transversely of the strip in order to set the strip width.
The cutting gap of the circular blade pairs and the blade overlap of the lower blade and upper blade, or upper blade and lower blade, of the trimming heads can be adjusted so as to minimize cutting burr and to extend the service life of the blades. It is important to generate the smallest possible cutting burr at the strip edge. The cutting burr is determined to a significant degree by the size of the cutting gap. Within the scope of the invention, the cutting gap refers to the distance between the blades in the strip plane, and thus normally to the horizontal cutting gap or the cutting gap in the axial direction, that is measured parallel to the rotation axes of the blades. The influence of the vertical overlap on quality or the size of the cutting burr has only a limited effect. The precise adjustment of the cutting gap or determination of the cutting gap during fabrication and processing of strip is thus of particular importance. However, the invention relates not only to trimmers but also other cutting apparatuses, e.g. cross-cutting shears.
Basically, it is known from practice to determine the cutting gap by measurement. In the heretofore known embodiment, one blade is mounted and horizontally fixed, while the other is horizontally adjustable, presuming of course that the strip is advanced horizontally perpendicular to a vertical plane or planes including the blade rotation axes. The position of the adjustable blade is measured, for example, using encoders. For purposes of calibration, the blades are moved together just far enough so that they just barely touch. This position of the encoder is stored and defined as the zero position for the cutting gap.
A disadvantage of the known procedure is that calibration of the cutting gap is done in part manually, and the assessment as to when the blades are just touching is subject to a certain degree of subjectivity. In addition, the calibration procedure takes a relatively long period of time. Furthermore, the cutting gap is not measured directly but from a certain distance due to design constraints. This aspect is particularly problematic when the machine is cool or at ambient temperature at the start of production, then heats up during production. The entire machine thus undergoes thermal expansion, thereby in turn affecting the cutting gap. In practice, it is thus necessary to recalibrate the machine several times as the machine heats up. If this is not done, the strip produced has highly variable quality in regard to the strip edge.